Spoiler
Liao Yin became a protector and subordinate of Ling Long after Ling Long reached the Body Integration level. Before that, she was a subordinate of Ao Xiao. Liao Yin signed a contract with Ao Xiao after he saved her. The contract stipulated that she would serve him for 100,000 years, and she fulfilled 60,000 years of service. Later, Ao Xiao decided to transfer this contract to Ling Long, so that Liao Yin would protect Ling Long for the remaining 40,000 years, knowing that he would not be able to pass the Heavenly Trial.